Mixed Base Conversion

Question

Background

Most people on here should be familiar with several base systems: decimal, binary, hexadecimal, octal. E.g. in the hexadecimal system, the number 12345₁₆ would represent

1*16^4 + 2*16^3 + 3*16^2 + 4*16^1 + 5*16^0

Note that we're usually not expecting the base (here, 16) to change from digit to digit.

A generalisation of these usual positional systems allows you to use a different numerical base for each digit. E.g. if we were alternating between decimal and binary system (starting with base 10 in the least significant digit), the number 190315_[2,10] would represent

1*10*2*10*2*10 + 9*2*10*2*10 + 0*10*2*10 + 3*2*10 + 1*10 + 5 = 7675

We denote this base as [2,10]. The right-most base corresponds to the least significant digit. Then you go through the bases (to the left) as you go through the digits (to the left), wrapping around if there are more digits than bases.

For further reading, see Wikipedia.

The Challenge

Write a program or function which, given a list of digits D an input base I and an output base O, converts the integer represented by D from base I to base O. You may take input via STDIN, ARGV or function argument and either return the result or print it to STDOUT.

You may assume:

• that the numbers in I and O are all greater than 1.
• the I and O are non-empty.
• that the input number is valid in the given base (i.e., no digit larger than its base).

D could be empty (representing 0) or could have leading zeroes. Your output should not contain leading zeroes. In particular, a result representing 0 should be returned as an empty list.

You must not use any built-in or 3rd-party base conversion functions.

This is code golf, the shortest answer (in bytes) wins.

Examples

D               I                  O        Result
[1,0,0]         [10]               [2]      [1,1,0,0,1,0,0]
[1,0,0]         [2]                [10]     [4]
[1,9,0,3,1,5]   [2,10]             [10]     [7,6,7,5]
[1,9,0,3,1,5]   [2,10]             [4,3,2]  [2,0,1,1,0,1,3,0,1]
[52,0,0,0,0]    [100,7,24,60,60]   [10]     [3,1,4,4,9,6,0,0]
[0,2,10]        [2,4,8,16]         [42]     [1,0]
[]              [123,456]          [13]     []
[0,0]           [123,456]          [13]     []

Answer 1

CJam, 45

q~_,@m>0@{@(:T+@T*@+}/\;La{\)_@+@@md@@j@+}jp;

Finally I found a good use of j.

How it works

Long ArrayList Block j executes the block which takes an integer as the parameter, and Long j will call this block recursively in the block. It will also store the values returned by the block in an internal array, which is initialized by the array parameter. It will not execute the block if the input is already in the array, and the value in the array is returned instead.

So if I initialize it with an array of an empty array, the empty array will be returned for input 0, and the block will be executed for any other input.

q~_,@m>0@{@(:T+@T*@+}/\;     " See below. Stack: O decoded-D ";
La                           " Initialized the value with input 0 as empty list. ";
{
  \)_@+@@md@@                " See below. Stack: remainder O quotient ";
  j                          " Call this block recursively except when the same quotient has
                               appeared before, which is impossible except the 0.
                               Stack: remainder O returned_list ";
  @+                         " Append the remainder to the list. ";
}j
p;                           " Format and output, and discard O. ";

CJam, 49 48

q~_,@m>0@{@(:T+@T*@+}/\;{\)_@+@@md@@}h;;_{}?]W%`

Input should be O I D.

Examples:

$ while read; do <<<$REPLY ./cjam-0.6.2.jar <(echo 'q~_,@m>0@{@(:T+@T*@+}/\;{\)_@+@@md@@}h;;_{}?]W%`');echo; done
[2] [10] [1 0 0]
[10] [2] [1 0 0]
[10] [2 10] [1 9 0 3 1 5]
[4 3 2] [2 10] [1 9 0 3 1 5]
[10] [100 7 24 60 60] [52 0 0 0 0]
[42] [2 4 8 16] [0 2 10]
[13] [123 456] []
[13] [123 456] [0 0]
[1 1 0 0 1 0 0]
[4]
[7 6 7 5]
[2 0 1 1 0 1 3 0 1]
[3 1 4 4 9 6 0 0]
[1 0]
""
""

How it works

q~           “ Read the input and evaluate. ";
_,@m>        " Rotate I to the right by the length of D. ";
0@{          " For each item in D, with the result initialized to 0: ";
  @(:T+      " Rotate I to the left, and set the original first item to T. ";
  @T*@+      " Calculate result * T + current. ";
}/
\;           " Discard I. ";
{            " Do: ";
  \)_@+      " Rotate O to the right, and get a copy of the original last item. ";
  @@md       " Calculate divmod. ";
  @@         " Move O and the quotient to the top of the stack. ";
}h           " ...while the quotient is not 0. ";
;;           " Discard O and the last 0. ";
_{}?         " If the last item is still 0, discard it. ";
]W%          " Collect into an array and reverse. ";
`            " Turn the array into its string representation. ";

Answer 2

CJam, 62 61 59 57 bytes

q~Wf%~UX@{1$*@+\@(+_W=@*@\}/;\;{\(+_W=@\md@@}h;;]W%_0=!>p

Reads the input arrays as [O I D] from STDIN. Try it online.

How it works

q~         " Read from STDIN and evaluate the input. Result: [O I D]                      ";
Wf%~       " Reverse each of the three arrays and dump them on the stack.                 ";
UX@        " Push U (0) and X (1); rotate D on top of both.                               ";
{          " For each N in D:                                                             ";
  1$*      "   N *= X                                                                     ";
  @+       "   U += N                                                                     ";
  \@(+     "   I := I[1:] + I[:1]                                                         ";
  _W=@*    "   X *= I[-1]                                                                 ";
  @\       "   ( U I X ) ↦ ( I U X )                                                      ";
}/         "                                                                              ";
;\;        " Discard I and X.                                                             ";
{          " R := []; Do:                                                                 ";
  \(+      "   O := O[1:] + O[:1]                                                         ";
  _W=@\md  "   R += [U / O[-1]], U %= O[-1]                                               ";
  @@       "   ( O U R[-1] ) ↦ ( R[-1] O U )                                              ";
}/         " While U                                                                      ";
;;]        " Discard U and O.                                                             ";
W%         " Reverse R.                                                                   ";
_0=!>      " Execute R := R[!R[0]:] to remove a potential leading zero.                   ";
p          " Print a string presentation of R.                                            ";

Test cases

$ cjam mixed-base.cjam <<< '[ [2]     [10]             [1 0 0]       ]'
[1 1 0 0 1 0 0]
$ cjam mixed-base.cjam <<< '[ [10]    [2]              [1 0 0]       ]'
[4]
$ cjam mixed-base.cjam <<< '[ [10]    [2 10]           [1 9 0 3 1 5] ]'
[7 6 7 5]
$ cjam mixed-base.cjam <<< '[ [4 3 2] [2 10]           [1 9 0 3 1 5] ]'
[2 0 1 1 0 1 3 0 1]
$ cjam mixed-base.cjam <<< '[ [10]    [100 7 24 60 60] [52 0 0 0 0]  ]'
[3 1 4 4 9 6 0 0]
$ cjam mixed-base.cjam <<< '[ [42]    [2 4 8 16]       [0 2 10]      ]'
[1 0]
$ cjam mixed-base.cjam <<< '[ [13]    [123 456]        []            ]'
""
$ cjam mixed-base.cjam <<< '[ [13]    [123 456]        [0 0]         ]'
""

Note that empty strings and empty arrays are indistinguishable to CJam, so []p prints "".

Answer 3

Python 2 - 318

from operator import *
d,i,o=input()
c=len
def p(l):return reduce(mul,l,1)
n=sum(x[1]*p((i[-x[0]%c(i)-1:]+x[0]/c(i)*i)[1:]) for x in enumerate(d[::-1]))
r=[]
j=1
t=[]
k=c(o)
while p(t)*max(o)<=n:t=(o[-j%k-1:]+j/k*o)[1:];j+=1
while j:j-=1;t=(o[-j%k-1:]+j/k*o)[1:];r+=[n/p(t)];n%=p(t)
print (r if r[0] else [])

I messed up the order of the arguments by accident, so I had to reverse them. I will work on the slice-fu to get the lists to work in the other direction later, I already wasted my entire lunch break :p

Fixed

Answer 4

Python 2 - 122

Very straightforward, didn't manage to find any special golf tricks on this one.

def f(D,I,O):
 n,i,l=0,-len(D),[]
 for d in D:n=n*I[i%len(I)]+d;i+=1
 while n:i-=1;b=O[i%len(O)];l=[n%b]+l;n/=b
 return l

Ungolfed:

def f(D,I,O):
    n = 0
    for i in range(len(D)):
        dn = len(D) - i
        n = n * I[-dn % len(I)] + D[i]
    l = []
    i = 0
    while n:
        i -= 1
        b = O[i%len(O)]
        l = [n%b] + l
        n /= b
    return l

Edit: 116-byte program version thanks to FryAmTheEggman

D,I,O=input()
n,i,l=0,-len(D),[]
for d in D:n=n*I[i%len(I)]+d;i+=1
while n:i-=1;b=O[i%len(O)];l=[n%b]+l;n/=b
print l

This version accepts comma-separated input e.g. [1,9,0,3,1,5], [2,10], [10]

Answer 5

APL, 78

{1↓(⊃1⌷⍺)({t←⍺[(⍴⍺)|⍴⍵]
(⌊0⌷⍵÷t)(t|0⌷⍵),1↓⍵}⍣{0=0⌷⍵}),+/(0,⍵)×⌽×\1,(⍴⍵)⍴⌽⊃0⌷⍺}

Examples:

f←{1↓(⊃1⌷⍺)({t←⍺[(⍴⍺)|⍴⍵]
  (⌊0⌷⍵÷t)(t|0⌷⍵),1↓⍵}⍣{0=0⌷⍵}),+/(0,⍵)×⌽×\1,(⍴⍵)⍴⌽⊃0⌷⍺}
(,10)(,2) f 1 0 0
1 1 0 0 1 0 0
(,2)(,10) f 1 0 0
4
(2 10)(,10) f 1 9 0 3 1 5
7 6 7 5
(2 10)(4 3 2) f 1 9 0 3 1 5
2 0 1 1 0 1 3 0 1
(100 7 24 60 60)(,10) f 52 0 0 0 0
3 1 4 4 9 6 0 0
(2 4 8 16)(,42) f 0 2 10
1 0
(123 456)(,13) f ⍬

⍴(123 456)(,13) f ⍬
0
(123 456)(,13) f 0 0

⍴(123 456)(,13) f 0 0
0

Answer 6

k2 - 83 74 char

Function taking one argument. This was just a lot better suited for K than J, which is why I'm not using J. It would just be a load of boxing/unboxing garbage, and nobody wants that. This is in the k2 dialect (may require some adaptation to work in the open source implementation Kona), but I'll change this to k4 if I can golf it down shorter there.

{:[#x@:|&~&\~x;|*{x 1}.[{_(x,y!*z;y%*z;1!z)}]/(();+/x*1*\(1-#x)#y;|z);()]}

I will note that I take a stand for pickiness here and say that one item lists have to be input as such. ,2 is a list of one item, that item being the scalar 2. Often scalars and 1-item lists are interchangable, but there is logic in this golf that relies on the assumption of list arguments.

To explain the golf, I'll break it into two parts. F is the golf, L is the main loop that calculates the output. The exact mechanism of the looping is that L is applied to its arguments repeatedly until the second argument is zero, then that result is returned. (This is the .[L]/ part.)

L: {_(x,y!*z;y%*z;1!z)}
F: {:[#x@:|&~&\~x;|*{x 1}.[L]/(();+/x*1*\(1-#x)#y;|z);()]}

By explosion:

{_(x,y!*z;y%*z;1!z)}  /function, args x y z
  (      ;    ;   )   / update each arg as follows:
               1!z    /  new z: rotate z left
            *z        /  head of z (current base digit)
          y%          /  y divided by that
 _                    /  new y: floor of that
     y!*z             /  y modulo head of z
   x,                 /  new x: append that to old x

{:[#x@:|&~&\~x;|*{x 1}.[L]/(();+/x*1*\(1-#x)#y;|z);()]}  /function, args x y z
            ~x                                           /find the 0s in x
          &\                                             /find leading zeros
        &~                                               /indices of digits that aren't
    x@ |                                                 /those items from x, reverse order
    x :                                                  /assign to x
 :[#          ;                                      ]   /if length is 0:
                                                   ()    / return empty list
                                                  ;      /else:
                      .[L]/                              / loop L repeatedly
                 {x 1}                                   / until y = 0
                           (  ;               ;  )       / starting with args:
                            ()                           /  Lx: empty list
                                       1-#x              /  number of input digits, minus 1
                                      (    )#y           /  cyclically extend base leftward
                                   1*\                   /  running product, start at 1
                                 x*                      /  multiply digits by these
                               +/                        /  Ly: sum of the above
                                               |z        /  Lz: out base, reverse order
               |*                                        / first elem of result, reversed

In action:

  {:[#x@:|&~&\~x;|*{x 1}.[{_(x,y!*z;y%*z;1!z)}]/(();+/x*1*\(1-#x)#y;|z);()]}[1 0 0; ,10; ,2]
1 1 0 0 1 0 0
  f:{:[#x@:|&~&\~x;|*{x 1}.[{_(x,y!*z;y%*z;1!z)}]/(();+/x*1*\(1-#x)#y;|z);()]}
  f[1 0 0; ,2; ,10]
,4
  f .' ((1 9 0 3 1 5; 2 10;           ,10)  /f apply each
>       (1 9 0 3 1 5; 2 10;           4 3 2)
>       (52 0 0 0 0;  100 7 24 60 60; ,10)
>       (0 2 10;      2 4 8 16;       ,42)
>       (();          123 456;        ,13)
>       (0 0;         123 456;        ,13))
(7 6 7 5
 2 0 1 1 0 1 3 0 1
 3 1 4 4 9 6 0 0
 1 0
 ()
 ())

Answer 7

Perl 6, 67 bytes

{[R,] [+]([R,](@^a)Z*1,|[\*] |[R,](@^b)xx*).polymod: |[R,](@^c)xx*}

Try it

Expanded:

{  # bare block lambda with placeholder parameters @a,@b,@c

  [R,]    # reduce the following using reverse meta op ｢R｣ combined with ｢,｣ op
          # (shorter than ｢reverse｣)

    [+](  # sum

        [R,](@^a) # reverse of first argument

      Z[*]        # zipped using &infix:<*> with the following

        1,
        |                    # slip the following in (flattens)
          [\*]               # triangle reduce

            |[R,](@^b) xx*   # reverse of second argument repeated infinitely
    )

    .polymod: |[R,](@^c) xx* # moduli the reverse of third argument repeated
}

---

In case you aren't sure what triangle reduce does:

[\*] 1,2,3,4,5
# 1, 1*2, 1*2*3, 1*2*3*4, 1*2*3*4*5
# 1,   2,     6,      24,       120

---

If I could take the inputs reversed, and output the reverse, it would be 47 bytes.

{[+](@^a Z*1,|[\*] |@^b xx*).polymod: |@^c xx*}

Try it